Open your \include\staff\newticket.inc.php file, and find this code around line 140:
<tr>
<td align="left" valign="top">Due Date:</td>
<td>
<i>Time is based on your time zone (GM <?=$thisuser->getTZoffset()?>)</i> <font class="error"> <?=$errors?></font><br>
<input id="duedate" name="duedate" value="<?=Format:($info)?>"
onclick="event.cancelBubble=true;calendar(this);" autocomplete=OFF>
<a href="#" onclick="event.cancelBubble=true;calendar(getObj('duedate'));"><IMG alt="blank" src="js/calendar.js"></IMG></script>
The javascript file itself was located on your \scp\js\ sub directory.
Sincerely,
Masino Sinaga